System and method for chemical mechanical polishing using retractable polishing pads

ABSTRACT

A chemical mechanical polishing includes a first spindle operable to rotate with respect to a central axis of the first spindle. A first polishing pad is coupled with the first spindle, and the first polishing pad has a first surface extending along a plane generally perpendicular to the central axis of the first spindle. A wafer carrier is included that is adapted to receive a wafer with a second surface generally parallel to the first surface of the first polishing pad. The wafer carrier is operable to rotate with respect to a central axis of the wafer carrier. The first surface of the first polishing pad is moveable along the central axis of the first spindle from a first position, wherein the first surface is spaced from the second surface, and a second position, wherein the first surface generally contacts the second surface.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates generally to the field of silicon wafer processing and more particularly, to a system and method for chemical mechanical polishing using retractable polishing pads.

BACKGROUND OF THE INVENTION

[0002] Chemical mechanical polishing (“CMP”) is a silicon wafer flattening and polishing procedure widely used in the fabrication of silicon wafers. CMP is used for polishing and/or flattening wafers after crystal growing, slicing and planarizing the wafer during the wafer fabrication process. As the name implies, there are two components to the process: chemical and mechanical polishing. Chemical polishing involves the introduction of chemicals that dissolve imperfections and impurities present upon the wafer. Mechanical polishing involves rotating the wafer upon an abrasive platen in order to grind the wafer to a predetermined thickness.

[0003] The wafers are typically mounted upside down on a holder and rotated above a pad sitting on a platen. The platen is also rotated. Typically, a slurry containing both chemicals and abrasives is introduced upon the platen.

[0004] Particular disadvantages associated with conventional chemical mechanical polishing methods include inconsistencies in polishing across the surface of the wafer, a lack of control of polishing forces and fluids and excess usage of polishing fluids and consumables.

SUMMARY OF THE INVENTION

[0005] The present invention provides a chemical mechanical polishing method and system using retractable polishing pads that substantially eliminates or reduces the problems and disadvantages associated with the previous methods and systems.

[0006] In accordance with a particular embodiment of the present invention, a method for polishing a silicon wafer includes polishing the silicon wafer with a first polishing pad and a second polishing pad at one time and moving the first polishing pad along a central axis of a first spindle that is coupled with the first polishing pad. The method also includes moving the second polishing pad along a central axis of a second spindle that is coupled with the second polishing pad.

[0007] In accordance with another embodiment, the first polishing pad is moved along a first axis that is generally perpendicular to the central axis of the first spindle. Furthermore, the second polishing pad may be moved along a second axis that is generally perpendicular to the central axis of the second spindle.

[0008] In accordance with another embodiment, an apparatus is provided comprising a first spindle operable to rotate with respect to a central axis of the first spindle. A first polishing pad is coupled with the first spindle, and the first polishing pad has a first surface extending along a plane generally perpendicular to the central axis of the first spindle. A wafer carrier is included that is adapted to receive a wafer with a second surface generally parallel to the first surface of the first polishing pad. The wafer carrier is operable to rotate with respect to a central axis of the wafer carrier. The first surface of the first polishing pad is moveable along the central axis of the first spindle from a first position, wherein the first surface is spaced from the second surface, and a second position, wherein the first surface generally contacts the second surface.

[0009] Technical advantages of particular embodiments of the present invention include a chemical mechanical polishing device that allows for the polishing of a silicon wafer by multiple polishing pads at one time. Each polishing pad may isolate and polish a particular area of the silicon wafer. Accordingly, the need for over-polishing certain areas of the silicon wafer is reduced, and reduced amounts of polishing fluids and consumables are needed.

[0010] Another technical advantage of particular embodiments of the present invention is a chemical mechanical polishing device with a single polishing pad that can accurately be directed to specific areas of the silicon wafer. Accordingly, unnecessary over-polishing of certain areas of the wafer can be avoided.

[0011] Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions and claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some or none of the enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention and its advantages, reference is now made to the following descriptions, taken in conjunction with the accompanying drawings, in which:

[0013]FIG. 1 is a diagram illustrating a chemical mechanical polishing machine in accordance with a particular embodiment of the invention;

[0014]FIG. 2A is an isometric diagram illustrating a chemical mechanical polishing machine in accordance with a particular embodiment of the invention;

[0015]FIG. 2B is an isometric diagram illustrating a chemical mechanical polishing machine in accordance with a particular embodiment of the invention; and

[0016]FIG. 3 is top view of a silicon wafer illustrating certain aspects of a particular embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a diagram illustrating a chemical mechanical polishing (“CMP”) machine in accordance with a particular embodiment of the present invention. CMP machine 10 includes a polishing pad holder 12 having spindles 14 extending therefrom. Each spindle 14 is coupled with polishing pad holder 12 at first end 13 and a polishing pad 16 at second end 17. FIG. 1 illustrates two spindles 14 and polishing pads 16; however, CMP machine may include only one or more than two spindles 14 and polishing pads 16. A wafer carrier 18 is disposed adjacent polishing pads 16, along a plane approximately perpendicular to central axes 15 of spindles 14. A silicon wafer 20 is coupled with wafer carrier 18 and disposed between polishing pads 16 and wafer carrier 18. Silicon wafer 20 is an example of the type of silicon wafer which may be polished, flattened and otherwise processed using CMP machine 10. In the illustrated embodiment, silicon wafer 20 is a thin, circular disk configuration. Silicon wafers of various sizes, shapes and configurations may be processed using CMP machine 10.

[0018] CMP machine 10 may be used for polishing and/or flattening silicon wafer crystals after growing, slicing and planarizing the wafer during the silicon wafer fabrication process. In the illustrated embodiment, each polishing pad 16 is configured to rotate in response to rotation of spindle 14 with respect to central- axis 15 of spindle 14. Wafer carrier 18 is configured to rotate during the polishing process with respect to central axis 19 of wafer carrier 18. Thus, silicon wafer 20 rotates as well. Each polishing pad 16 is extendable and retractable along central axis 15 of its respective spindle 14. Accordingly, each polishing pad 16 may contact the surface of silicon wafer 20. The rotation and movement of polishing pads 16, combined with the rotation of wafer carrier 18, allow for the polishing of silicon wafer by multiple polishing heads 16 at one time. Polishing heads 16 polish and grind the silicon wafer to provide a clean, flat surface on the silicon wafer.

[0019] CMP machine 10 may include independent controllers 22 which control the movement of a respective polishing pad 16. An operator can independently control the movement of each polishing pad 16 through its respective controller 22. Endpoint detection systems 24 detect the location of a respective polishing pad 16 with respect to silicon wafer 20. Endpoint detection systems 24 may also monitor thickness, planarity and other characteristics of silicon wafer 20 at such locations.

[0020] Fluid delivery dispensers 26 provide a liquid slurry to silicon wafer 20 adjacent each polishing pad 16 to enhance the polishing process. The liquid slurry may include acids and other chemicals which interact with silicon wafer 20 in order to loosen, and at least partially remove, metals, oxides and other impurities present upon silicon wafer 20. The liquid slurry may also include small particles of glass or other abrasive materials. These abrasive materials grind silicon wafer 20 in response to friction caused by rotation and movement of polishing pads 16 and rotation of wafer carrier 18, during the polishing process. An operator of CMP machine 10 may control the dispensation of varying amounts of liquid slurry adjacent or through each polishing pad as needed for the polishing process.

[0021] Deionized water delivery dispensers 28 provide deionized water or a combination of deionized water and a pH controlling substance to silicon wafer 20 adjacent each polishing pad 16 to enhance the polishing process. An operator of CMP machine 10 may control the dispensation of varying amounts of deionized water or other substance through deionized water delivery dispensers 28 adjacent or through each polishing pad as needed for the polishing process.

[0022]FIGS. 2A and 2B are isometric diagrams, with portions broken away, of a CMP machine 110 in accordance with another embodiment of the present invention. FIG. 2A shows four polishing pads 116. Each polishing pad 116 is coupled to a respective spindle 114 at end 117 of spindle 114. Wafer carrier 118 of FIG. 2B receives silicon wafer 120 disposed proximate polishing pads 116. Each polishing pad 116 rotates with respect to a central axis 115 of its respective spindle 114 in directions generally indicated by arrows 130; however, each polishing pad 116 need not rotate in both general directions indicated by arrows 130. Polishing pads 116 are extended or retracted along central axes 115 in directions generally indicated by arrows 132. Such movement brings polishing pads 116 into contact with silicon wafer 120. Wafer carrier 118 rotates with respect to central axis 119 of wafer carrier 118 in the general directions indicated by arrow 136; however, wafer carrier 118 need not rotate in both general directions indicated by arrow 136.

[0023] Each polishing pad 116 may contact silicon wafer 120 at a respective zone of influence 138-141 of silicon wafer 120. Each polishing pad 116 is responsible for polishing a specific zone of influence of silicon wafer 120. Each polishing pad 116 moves along an axis 121 which is generally perpendicular to central axis 115 of its respective spindle 114. Such movement may be in directions generally indicated by arrows 134. It should be understood that axes 121 may be aligned in any number of directions while still generally perpendicular to central axes 115, and thus, arrows 134 may be directed towards other directions which correspond to axes 115. Movement of each polishing pad 116 along axes 115 and 121 as well as rotational movement of each polishing pad 116 and wafer carrier 118 with respect to central axes 115 and 119, respectively, result in the polishing and grinding of one silicon wafer 120 by multiple polishing pads 116 at one time. End point detection systems 124 detect the location of a respective polishing pad 116 with respect to silicon wafer 120 and can take various measurements including, without limitation, thickness and planarity at such location on silicon wafer 120 before, during and after the polishing process. In other embodiments, more than one polishing pad may be responsible for polishing a particular zone of influence.

[0024] Each polishing pad 116 is associated with a controller 122 which controls the movement of the polishing pad 116. An operator may use information collected by endpoint detection systems 124 to selectively control the movement of such controller's respective polishing pad 116. The movement of each polishing pad 116 can be controlled to polish a particular location or zone of influence of silicon wafer 120 to a desired degree or to correct an undesired or irregular edge condition upon a specific location or zone of influence. This can be done even while an operator is using another controller 122 to control the movement of another polishing pad 116 on a separate zone of influence at the same time. Zones of influence 138-141 may each be polished at the same time by separate polishing pads 116 in this manner. Furthermore, the operator can use measurements taken by endpoint detection systems 124 to determine to what degree to polish and grind each zone of influence 138-141.

[0025] The use of separate polishing pads 116 on a single silicon wafer 120 at one time allows each polishing pad 116 to pinpoint local regions of silicon wafer 120 through its respective endpoint detection system 124 for optimal film uniformity and polish control. This may result in a reduced need for over-polishing certain areas of silicon wafer 120. Furthermore, consumables such as liquid slurry and deionized water can be dispensed with respect to the particular polishing pad 116 that needs them through fluid delivery dispensers 126 and deionized water delivery dispensers 128, respectively. This reduces the amount of consumables that are needed.

[0026]FIG. 3 is a top view illustrating particular aspects of a CMP machine in accordance with another embodiment of the present invention. Polishing pads 150-154 polish zones of influence 160-164, respectively, of silicon wafer 180. Each polishing pad is responsible for polishing a respective zone of influence; for example, polishing pad 150 polishes zone of influence 160, polishing pad 151 polishes zone of influence 161, polishing pad 152 polishes zone of influence 162, polishing pad 153 polishes zone of influence 163 and polishing pad 154 polishes zone of influence 164. The concentric circle configuration of zones of influence 160-164 is beneficial since it corresponds with the circular disk shape of silicon wafer 180. For most applications, an operator will be interested in achieving a completely flat planar surface across silicon wafer 180. Since silicon wafer 180 rotates with a wafer carrier, the use of any polishing pad 150-154 can polish and grind the entire circular-ring shaped zone of influence with which that polishing pad is associated. In the illustrated embodiment, five polishing heads corresponding to five zones of influence are shown. The number, size, shape and configuration of zones of influence 160-164 may be significantly altered within the teachings of the present invention. Each polishing pad may move along silicon wafer 180 in a linear direction generally indicated by arrows 184 and may also rotate and move in a direction generally perpendicular to the surface of silicon wafer 180 as discussed previously.

[0027] In other embodiments, more than one polishing pad may be responsible for polishing a particular zone of influence. A particular polishing pad may also be responsible for polishing more than one zone of influence.

[0028] The portions of CMP machine 10 illustrated in FIGS. 1 through 3 are shown to illustrate the type of CMP equipment which may incorporate aspects of the present invention. Various other CMP equipment is available for use within the teachings of the present invention. It will be recognized by those of ordinary skill in the art that the type of CMP machine, along with the size, shape and configuration of the various components illustrated including, without limitation, the spindle, polishing pad, polishing pad holder, wafer carrier, silicon wafer, fluid delivery dispenser, deionized water delivery dispenser, controller and/or endpoint detection system may be varied within the teachings of the present invention.

[0029] Although the present invention has been described in detail, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as falling within the scope of the appended claims. 

What is claimed is:
 1. An apparatus, comprising: a first spindle operable to rotate with respect to a central axis of the first spindle; a first polishing pad coupled with the first spindle, the first polishing pad having a first surface extending along a plane generally perpendicular to the central axis of the first spindle; a wafer carrier adapted to receive a wafer, the wafer having a second surface generally parallel to the first surface of the first polishing pad, the wafer carrier operable to rotate with respect to a central axis of the wafer carrier; and wherein the first surface is moveable along the central axis of the first spindle from a first position wherein the first surface is spaced from the second surface, and a second position wherein the first surface generally contacts the second surface.
 2. The apparatus of claim 1, wherein the first surface is moveable along a first axis generally perpendicular to the central axis of the first spindle.
 3. The apparatus of claim 1, further comprising: a second spindle operable to rotate with respect to a central axis of the second spindle, the central axis of the second spindle being approximately parallel to the central axis of the first spindle; and a second polishing pad coupled with the second spindle, the second polishing pad being moveable along the central axis of the second spindle to a third position in which the second polishing pad generally contacts the second surface.
 4. The apparatus of claim 3, wherein the second polishing pad is moveable along a second axis generally perpendicular to the central axis of the second spindle.
 5. The apparatus of claim 3, wherein the first and second polishing pads each generally contact the second surface at one time.
 6. The apparatus of claim 3, further comprising independent first and second controllers operable to control movement of the first and second polishing pads, respectively.
 7. The apparatus of claim 3, further comprising first and second endpoint detection systems operable to detect the locations of the first and second polishing pads, respectively, with respect to the second surface.
 8. The apparatus of claim 3, further comprising independent first and second fluid delivery dispensers operable to provide fluids to first and second locations adjacent the first and second polishing pads, respectively.
 9. The apparatus of claim 3, further comprising independent first and second deionized water delivery dispensers operable to provide deionized water to first and second locations adjacent the first and second polishing pads, respectively.
 10. The apparatus of claim 3, wherein the first polishing pad and the second polishing pad apply downward forces upon the second surface.
 11. The apparatus of claim 10, further comprising independent first and second controllers operable to control application of downward forces upon the second surface by the first and second polishing pads, respectively.
 12. The apparatus of claim 1, wherein the first surface has a diameter less than a diameter of the second surface.
 13. The apparatus of claim 12, wherein the diameter of the first surface is approximately one-sixteenth the diameter of the second surface.
 14. The apparatus of claim 12, wherein the diameter of the first surface is approximately 0.75 inches.
 15. An apparatus, comprising: a first spindle operable to rotate with respect to a central axis of the first spindle; a first polishing pad coupled with the first spindle, the first polishing pad having a first surface extending along a plane generally perpendicular to the central axis of the first spindle; the first surface moveable along a first axis, the first axis generally perpendicular to the central axis of the first spindle; a second spindle operable to rotate with respect to a central axis of the second spindle; a second polishing pad coupled with the second spindle; the second polishing pad moveable along a second axis, the second axis generally perpendicular to the central axis of the second spindle; and a wafer carrier having a second surface generally parallel to the first surface of the first polishing pad, the second surface operable to rotate with respect to a central axis of the wafer carrier, the second surface being adapted to receive a wafer.
 16. The apparatus of claim 15, wherein: the first surface is moveable along the central axis of the first spindle from a first position wherein the first surface is spaced from the second surface and a second position wherein the first surface generally contacts the second surface; and the second polishing pad is moveable along the central axis of the second spindle to a third position in which the second polishing pad generally contacts the second surface.
 17. The apparatus of claim 16, wherein the first and second polishing pads each generally contact the second surface second surface at one time.
 18. The apparatus of claim 15, further comprising independent first and second controllers operable to control movement of the first and second polishing pads.
 19. The apparatus of claim 15, further comprising first and second endpoint detection systems operable to detect the locations of the first and second polishing pads, respectively, with respect to the second surface.
 20. The apparatus of claim 15, further comprising independent first and second fluid delivery dispensers operable to provide fluids to first and second locations adjacent the first and second polishing pads, respectively.
 21. The apparatus of claim 15, further comprising deionized water delivery systems operable to provide deionized water to first and second locations adjacent the first and second polishing pads, respectively.
 22. The apparatus of claim 15, wherein the first surface has a diameter less than a diameter of the second surface.
 23. The apparatus of claim 22, wherein the diameter of the first surface is approximately one-sixteenth the diameter of the second surface.
 24. The apparatus of claim 22, wherein the diameter of the first surface is approximately 0.75 inches.
 25. A method for polishing a silicon wafer, comprising: polishing the silicon wafer with a first polishing pad and a second polishing pad at one time, the silicon wafer having a first surface; moving the first polishing pad along a central axis of a first spindle, the first spindle coupled with the first polishing pad; and moving the second polishing pad along a central axis of a second spindle, the second spindle coupled with the second polishing pad.
 26. The method of claim 25, further comprising: moving the first polishing pad along a first axis, the first axis generally perpendicular to the central axis of the first spindle; and moving the second polishing pad along a second axis, the second axis generally perpendicular to the central axis of the second spindle.
 27. The method of claim 25, further comprising controlling the movement of the first polishing pad and the second polishing pad with independent first and second controllers, respectively.
 28. The method of claim 25, further comprising monitoring a first thickness of the silicon wafer at a first location on the wafer and a second thickness of the silicon wafer at a second location on the wafer with first and second endpoint detection systems, respectively, wherein first and second endpoint detection systems are adjacent first and second polishing pads, respectively.
 29. The method of claim 28, further comprising adjusting the locations of the first polishing pad and the second polishing pad along the central axis of the first spindle and the central axis of the second spindle, respectively, based upon the first thickness and the second thickness.
 30. The method of claim 25, further comprising providing fluids to the first surface of the silicon wafer with first and second fluid delivery dispensers, wherein first and second fluid delivery dispensers are adjacent first and second polishing pads, respectively.
 31. The method of claim 25, wherein the first polishing pad has a second surface having a diameter less than a diameter of the first surface of the silicon wafer.
 32. The method of claim 31, wherein the diameter of the second surface is approximately one-sixteenth the diameter of the first surface.
 33. An apparatus, comprising: first, second, third and fourth spindles operable to rotate with respect to respective central axes of the first, second, third and fourth spindles; first, second, third and fourth polishing pads coupled with the first, second, third and fourth spindles, respectively, the first polishing pad having a first surface extending along a plane generally perpendicular to the central axis of the first spindle; a wafer carrier disposed below the first, second, third and fourth polishing pads, the wafer carrier operable to rotate with respect to a central axis of the wafer carrier, the wafer carrier adapted to receive a silicon wafer, the silicon wafer having a second surface extending along a plane generally parallel to the first surface of the first polishing pad, the second surface having a diameter approximately sixteen times a diameter of the first surface; the first, second, third and fourth spindles further operable to move along the respective central axes of the first, second, third and fourth spindles, to respective first, second, third and fourth positions, in which the first, second, third, and fourth spindles generally contact the second surface; the first, second, third and fourth spindles further operable to move along respective first, second, third and fourth linear axes, wherein the first, second, third and fourth linear axes are generally perpendicular to the central axis of the first spindle; the first, second, third and fourth polishing pads each generally contact the second surface at one time; first, second, third and fourth endpoint detection systems operable to detect the locations of the first, second, third and fourth polishing pads, respectively, with respect to the second surface; first, second, third and fourth controllers operable to control movement of the first, second, third and fourth polishing pads, respectively; first, second, third and fourth fluid delivery dispensers operable to provide fluids to the second surface adjacent the first, second, third and fourth polishing pads, respectively; and first, second, third and fourth deionized water delivery dispensers operable to provide deionized water to the second surface adjacent the first, second, third and fourth polishing pads, respectively.
 34. A method for polishing a silicon wafer, comprising: polishing the silicon wafer with first, second, third and fourth polishing pads at one time, the silicon wafer having a first surface; moving the first, second, third and fourth polishing pads along respective central axes of the first, second, third and fourth polishing pads; moving the first, second, third and fourth polishing pads along respective first, second, third and fourth axes, the first, second, third and fourth axes generally perpendicular to the central axis of the first polishing pad; controlling the movement of the first, second, third and fourth polishing pads with independent first, second, third and fourth controllers, respectively; monitoring first, second, third and fourth thicknesses of the silicon wafer at first, second, third and fourth locations, respectively, with first, second, third and fourth endpoint detection systems, respectively, wherein first, second, third and fourth endpoint detection systems are adjacent first, second, third and fourth polishing pads, respectively; adjusting the locations of the first, second, third and fourth polishing pads along the respective central axes of the first, second, third and fourth spindles, based upon the first, second, third and fourth thicknesses, respectively; and providing fluids to the first surface of the silicon wafer with first, second, third and fourth fluid delivery dispensers, wherein first, second, third and fourth fluid delivery dispensers are adjacent first, second, third and fourth polishing pads, respectively. 